Nanoscale variable resistor/electromechanical transistor

ABSTRACT

A nanoscale variable resistor including a metal nanowire as an active element, a dielectric, and a gate. By selective application of a gate voltage, stochastic transitions between different conducting states, and even length, of the nanowire can be induced and with a switching time as fast as picoseconds. With an appropriate choice of dielectric, the transconductance of the device, which may also be considered an “electromechanical transistor,” is shown to significantly exceed the conductance quantum G0=2e 2 /h.

This application claims the benefit of the filing date of U.S.Provisional Patent Application No. 60/937,329, filed Jun. 27, 2007,which is entirely incorporated by reference.

The U.S. Government has certain rights in this invention pursuant to NSFgrant Numbers 0312038, PHY-0651077 and PHY-0601179.

This invention is directed toward a method and system for producing ananoscale variable resistor. More particularly, the invention isdirected to a nanoscale resistor comprised of an active metal nanowire,a dielectric and a gate. A voltage pulse from the gate enables acontrolled stochastic transition between selectable conducting states ofthe nanowire and can be switched in the pico-second range.

BACKGROUND OF THE INVENTION

Metal nanowires have attracted considerable interest in the past decadedue to their remarkable transport and structural properties. Gold andsilver nanowires were observed to form spontaneously under electronirradiation, and appear to be stable. Even the thinnest gold wires,essentially chains of atoms, have been observed to exhibit lifetimes ofthe order of seconds at room temperature. Metal nanowires exhibitstriking correlations between their stability and electricalconductance. Although not limiting the scope of the invention, thestability of filamentary structures can be explained by electron-shelleffects. Because most of the atoms of a nanowire are at the surface,with low coordination numbers, metal nanowires behave essentially likefluids. Classically, the Rayleigh instability would break up any wirewhose length exceeds its circumference. Nevertheless, nanowiresviolating the Rayleigh criterion have been observed. The instability issuppressed through quantum effects, with stabilization occurring throughthe nanowire's electronic shell structure. A quantum linear stabilityanalysis showed the existence of “islands of stability” for discreteintervals of the radius R. These correspond to conductance “magicnumbers” that agree with those observed in experiments. For low enoughtemperatures, there remain finite regions of R stable againstlong-wavelength perturbations. Therefore, stable wires exist only in thevicinity of certain “magic radii” and consequently at quantizedconductance values G that are integer multiples of the conductancequantum G₀=2e²/h. However, this linear stability analysis ignores largethermal fluctuations that can lead to breakup of the wire. Nanowirelifetimes are inferred from conductance histograms which are compiled bycycling a mechanically controllable break junction thousands of times.Prior art studies indicate that conductance peaks disappear above fairlywell-defined temperatures.

The lifetimes of these nanowires have been studied in the art by usingconventional techniques. By modeling thermal fluctuations throughstochastic Ginzburg-Landau classical field theories, a self-consistentapproach has been constructed to provide an explanation of thefluctuation-induced “necking” of nanowires that is in good agreementwith prior art experiments. This theory indicates that passivated noblemetal nanowires are sufficiently stable at room temperature to serve asinterconnects between nanoscale circuit elements.

On the experimental side, nanowires with diameters less than a nanometerhave been directly observed using transmission electron microscopes(TEM) to remain stable under low beam intensities below 5 A/cm² for theduration of observation. Stochastic switching between differentconductance values has been observed in contacts made using mechanicallycontrollable break junctions, while controllable switching has beenachieved recently using electromigration to grow or Shrink a nanobridgebetween two wires. A structural thinning process of the nanowire similarto the one described by the theory of Bürki et al. has been observed totake place for gold nanowires in TEM experiments. The nanowire wasobserved to thin step by step via a process where a structural step(corresponding to a change in radius of the order of one atomicdiameter) forms at one end of the wire and subsequently propagates alongthe wire.

Nanowires suitable for the proposed device, i.e. with conductancebetween a few and a hundred conductance quanta, and lengths below oraround a few nanometers have been realized experimentally using varioustechniques:

a. Scanning tunneling microscopy (STM) In this technique, a STM tip iscrashed into a metal sample, thus forming a nanocontact. The size, andthus conductance, of the metal contact can then be adjusted to apredefined value by adapting the tip-sample distance. This technique hasbeen shown to form relatively short wires down to atomically thin crosssections. However, it is sensitive to drift in the STM tip position, aswell as to external vibrations. Furthermore, it is limited to metalswhich can be used to fabricate a sharp tip (Au, W, and other metalsknown in the art to be fabricable). However, a STM tip could be used tocontrol strain on a longer, preformed nanowire, thus inducingconductance changes.

b. Mechanically controllable break-junction (MCBJ) With this technique,a macroscopic wire is glued to a support, itself mounted on athree-point bending device. A notch in the macroscopic wire provides aweak point where the wire breaks upon bending of the substrate. Ananocontact is formed, and its size can be controlled by adjusting thebending of the substrate. As for the STM technique, relatively shortwires are formed, but the setup is more stable (i.e. less sensitive toexternal vibrations) and more versatile, as essentially any metal can beused. However, the need for such a three-point bending device, whileallowing control of the strain applied to a nanowire, makes it difficultto have a fully nano-sized device.

c. Thin-film transmission electron microscopy (TEM) In contrast to theprevious techniques, long wires can be formed by burning holes into athin metallic film deposited on a substrate, using a strong electronirradiation. When two holes come close together, the irradiationintensity is decreased, switching the TEM to imaging mode, and a thinbridge is left, and is seen to self-assemble into a long, almostperfectly cylindrical wire. The nanowire thus formed is found to besuspended above the substrate, and has typically a diameter between halfand a few nanometers, and a length of several nanometers. There is up tonow little control on the final size of the wire, which is seen to bestable for seconds or longer at room temperature. As an alternative, ascanning electron microscope (SEM) could be used rather than TEM.

d. Electromigration and electrochemical fabrication. These two methodshave been developed recently, and the wire size can be controlled in theformer case by electromigration due to a voltage across the wire, or inthe latter case by an electrochemical potential which controls etchingfrom, or deposition on the wire through an electrolyte, while thepresence of the electrolyte has been shown to have little influence onthe stability and transport properties of the wire. Both methods havebeen shown to allow good control of the conductance of the wire. Theelectromigration technique has been generalized to create severalcontacts of similar size in parallel.

In order to change a nanowire configuration, several methods have beeninvestigated: raising the temperature, applying strain and shorteningthe wire. For the purposes of a useful nanoscale device, these prior artmethods are unsatisfactory for various reasons, principally having to doeither with nonoptimal operating conditions (temperature), or inabilityto implement these controls on the nanoscale (strain). However, none ofthe prior art methodologies described hereinbefore enables creation ofstable nanowires which can be rapidly and controllably switched betweendifferent conductance states.

SUMMARY OF THE INVENTION

Variable resistors are commonly used circuit elements in many electronicapplications. However, their large size and slow response time haveheretofore limited their use primarily to the human-circuit interface.In order to establish a reliable nanoswitch for uses, such as, but notlimited to, a nanoscale variable resistor and transistor, we describeherein the exploitation of quantum and stochastic effects at thenanoscale to allow one to combine what would ordinarily be distinctmacroscale circuit elements into a single nanoscale device with multiplefunctionalities, and to achieve response times on the order ofpicoseconds.

These and other objects, advantages and features of the invention,together with the organization and manner of operation thereof, willbecome apparent from the following detailed description when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: illustrates a schematic diagram of a representative embodimentof the invention device;

FIG. 2: illustrates electron-shell potential as a function of wireradius k_(F) R wherein the conductance of the wires with “magic radii”is indicated on the top axis;

FIG. 3: illustrates calculated escape barrier as a function of wireradius k_(F) R or equivalently applied stress F and results correspondto a gold wire with a conductance G=17 G₀;

FIG. 4A: illustrates escape barrier ΔE (top) and prefactor Γ₀ (bottom)as a function of wire length and a second-order phase transition takesplace at the critical length L_(c) and for some wires, the transition isfirst-order (see inset FIG. 4B).

FIG. 5A: illustrates conductance of a short wire (solid line) and longwire (dashed line) under compression and the initial (left-hand-side)and final (right-hand-side) shapes of the long (B) and short (C) wiresare shown in the inset FIG. 5B (long wire) and FIG. 5C (short wire);

FIG. 6A: illustrates a device in cross-section of the invention using asolid dielectric and FIG. 6B shows a longitudinal cross-sectional viewof FIG. 6A;

FIG. 7A: illustrates a cross-section view of a device of the inventionusing liquid dielectric in a cavity and FIG. 7B shows the device in aside view;

FIG. 8A: illustrates a cross-section view of a device of the inventionusing a drop of liquid dielectric and FIG. 8B shows a top view of thedevice;

FIG. 9A: illustrates a cross-section view of a device of the inventionusing a solid dielectric with a top gate and FIG. 9B shows alongitudinal cross-section view of the device;

FIG. 10; illustrates an array of devices with top and bottom gates;

FIG. 11; illustrates an array of devices with top and bottom gates (topview) and

FIG. 12: illustrates an alternate embodiment of an array of devices withtop and bottom gates (top view).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In one embodiment of the invention, a device 90 is illustratedschematically in FIG. 1. A metal nanowire 100 is an active circuitelement of the device 90 and is embedded in a dielectric sheath 110,surrounded by an outer conductor 120 of comparable dimensions, which isreferred to hereinafter as the gate 120. In a preferred embodiment thegate 120 is coupled electrostatically to the nanowire 100 to effectswitching. For optimal functionality, in a preferred embodiment, thedielectric constant ∈ for appropriate dielectric materials should exceedapproximately ten (example dielectric materials are, Si, Ge, InSb, InAs,InP, GaSb, or GaAs). The dielectric sheath 110 should preferably fill tothe maximum extent possible the region between the nanowire 100 and thegate 120. A liquid dielectric form of the sheath 110 can be particularlysuitable regarding both of these requirements, with e.g., water having adielectric constant ∈ which equals about 80. Alternately, a dielectricgel or sol-gel could be used. A positive/negative voltage applied to thegate 120 selectively can enhance/deplete the density of carriers in thenanowire 100. Importantly, the resulting shift in the Fermi energy E_(F)alters the electron-shell structure of the nanowire 100, which in turndetermines its stability.

The electron-shell potential is shown in FIG. 2; it exhibits severalminima as a function of the dimensionless parameter k_(F) R, with k_(F)the Fermi wavevector and R the wire radius. A shift in k_(F) is thusanalogous to applying strain, and can selectively be used to inducerapid (i.e., on the scale of the Debye frequency) transitions betweenneighboring magic radii. These have conductances differing by nG₀, wheren≧2 is an integer (see FIG. 2). As a rule of thumb, the jumps betweenthe electron shell potential minima scale as n ˜(π/4)k_(F)R for a formof the wire 100 with initial radius R. The switching time between twoadjacent “magic radii” (minima of the electron-shell potential) wasshown to be given by the Kramers formula,τ˜Γ₀ ⁻¹exp(ΔE/k_(B)T),  (1)where ΔE is the energy barrier, k_(B) is Boltzmann's constant, and T isthe temperature. The rate prefactor Γ₀, of order the Debye frequency,has been calculated in the prior art. The dependence of ΔE on theparameter k_(F) R is illustrated in FIG. 3.

The possibility of shifting E_(F) electrostatically, as described above,depends in an essential way on the crucial feature that the nanowire 100has a radius of order nanometers, and thus has a very low density ofstates at E_(F). As a function of the applied gate voltage V_(g), theshift in E_(F) is given by,

$\begin{matrix}{{{\delta\; E_{F}} = \frac{e\;\delta\; V_{g}}{1 + {\left( {e^{2}/C_{g}} \right){{\mathbb{d}N}/{\mathbb{d}E}}}}},} & (2)\end{matrix}$

where C_(g) is the mutual capacitance between the gate 120 and thenanowire 100, and dN/dE is the density of states of the nanowire 100 atE_(F). The denominator in Eq. (2) can be well approximated in terms ofmaterial and geometrical parameters, yielding a convenient rule-of-thumbestimate,

$\begin{matrix}{{{\delta\; E_{F}} \approx \frac{e\;\delta\; V_{g}}{{1 + {\alpha\; r_{x}}} \in^{- 1}{G/G_{0}}}},} & (3)\end{matrix}$where r_(s) is the Fermi gas parameter for the nanowire material(essentially the mean inter-electron separation in the bulk metal), andα is a dimensionless parameter of order unity, which dependslogarithmically on the device dimensions (sec FIG. 1).

In order to achieve the maximum switching speed, it is necessary toachieve a shift. δ(k_(F)R)˜1 in the shell-potential parameter. From Eq.(3), this implies a preferred operating gate voltage,

$\begin{matrix}{{\left. \frac{e\; V_{g}}{E_{F}} \right.\sim\frac{\alpha\; r_{s}k_{F}R}{6 \in}}.} & (4)\end{matrix}$

For typical metals, r_(s)˜2-3, while k_(F) R˜10 in the domain ofvalidity of the nanoscale free electron model. In a most preferredembodiment, it is therefore desirable to use a dielectric with ∈≧10 tominimize the necessary gate voltages.

Because the “mechanical” switching time of the nanoscale variableresistor can be as short as picoseconds, it can also be thought of as anelectromechanical transistor. It is thus useful to establish itstransconductance, a figure of merit used to characterize transistors.The transconductance g_(r) can be estimated as

$\begin{matrix}{g_{T} = {{\left. \frac{\mathbb{d}I_{1}}{\mathbb{d}V_{g}} \right.\sim\frac{{nG}_{0}V_{12}}{V_{g}}}.}} & (5)\end{matrix}$

Using Eq. (4) and n˜(π/4)k_(F) R, one finds,

$\begin{matrix}{{\left. \frac{g_{T}}{G_{0}} \right.\sim\frac{{3\pi} \in}{2\alpha\; r_{s}}}{\frac{e\; V_{12}}{E_{F}}.}} & (6)\end{matrix}$

For large dielectric constants ∈≧10, and bias voltages V₁₂˜1V, one canthus achieve g_(r)>>G₀, an exceptional figure of merit for a nanoscaledevice, thereby enabling its advantageous use as an effectivetransistor. The device 90 discussed above is one where barriers arecontrolled by shifting the Fermi energy of the nanowire 100 throughelectrostatic means. In addition to the structural switching time oforder picoseconds, the electrical RC rise time t=C_(g)/G can beestimated to be of order 1 femtosecond for typical devicedimensions/materials, and so is not a limiting factor in deviceperformance.

Another aspect of the invention can be shown by considering the changingof the wire length. A transition in activation behavior can occur as afunction of wire length; below a critical length L_(c), the barrierdecreases rapidly with length, while above it is roughly constant. Thetransition can be continuous (second-order) or discontinuous(first-order) (see FIG. 4). This effect may have already been observedin a recent study which has reported a transition from linear tononlinear I-V behavior in gold nanowires, as distance between electrodesshortened due to applied bias. We have been able to explain this resultas a consequence of the transition in radius stability as a function ofwire length (see FIG. 4). This observation leads to another devicepossibility, namely changing wire length directly by changing theapplied voltage. This would convert the wire 100 with linear I-Vcharacteristics to one with nonlinear ones. This is illustrated in FIGS.5A-C which shows a model calculation of the wire shape and conductanceduring compression. FIG. 5B shows a wire whose length exceeds thecritical length L_(c); under compression (e.g. due to heating of thecontacts under finite bias) its radius is stable, and its conductance(shown as a dashed line in FIG. 5A) remains constant. FIG. 5C shows ashorter wire whose length is close to L_(c); its radius is unstable andincreases under compression, together with the wire conductance shown asa solid, line in FIG. 5A.

In a preferred embodiment, commercial fabrication of the nanoscalevariable resistor/electromechanical transistor device 90 includescombining the three components of the device 90, the metal nanowire 100,the dielectric sheath 110, and the gate 120 and integrated with othercircuitry on a chip (not shown). Accordingly, in one preferredembodiment of the current invention, the production of the nanoscalecircuitry is based on performing the following four (4) steps:

Step 1: The initial structure of the nanowire 100, including itselectrical connection to the rest of an integrated circuit 130 (see FIG.1), can be formed with standard semiconductor fabrication and patterningprocesses such as for example E-beam direct write, or alternatively inthe long term masked ion beam lithography, to deposit a metal wire tensof nanometers in diameter on the substrate (e.g., a Si wafer or otherinsulating substrate). Suitable example metals for nanowire formationinclude Au, Ag, Cu, Pt, and Al, among others. Any elemental metal (notalloy) of sufficient stability, and sufficiently ductile can be used toform nanocontacts.

Step 2: To form an active form of the device 90, a short section of thenanowire 100 preferably is thinned down to a diameter of order onenanometer using one of the known nanowire fabrication techniquesoutlined above, such as a focused scanning electron microscope (SEM),electromigration, or chemical etching.

Step 3: The active segment of the nanowire 100 is encased in thedielectric sheath 110, which also serves to passivate the nanowiresurface, increasing durability.

Step 4: Finally, the nanowire 100 encased in the dielectric sheath 110is placed in proximity to one or more of the metal gates 120 which isused to control the nanowire resistance through induced structuraltransitions.

In a most preferred embodiment, to achieve optimal devicecharacteristics, the space around the active segment of the nanowire 100should be filled with the dielectric sheath 110 having ∈≧10. If a solidform of the dielectric sheath 110 (only) is used, a small gap 210 aroundthe active segment of the nanowire 100 is provided (see FIG. 6B) topermit the nanowire surface to fluctuate freely. FIGS. 6A and 6B are twodifferent views of the same device. The wire fills the gap in FIG. 6Abecause the cross section shows the thicker part of the wire, whichhides the thinner part, both of which are visible in FIG. 6B. In thatcase, the mean dielectric constant of the region between the nanowire100 and the gate(s) 120 on substrate 150 (including the gap) shouldpreferably exceed ten. Many intrinsic semiconductors could serve assuitable solid dielectrics with ∈≧10 (e.g., Si, Ge, InSb, InAs, InP,GaSb, or GaAs). The material should be chosen so that the semiconductingenergy gap exceeds the maximum desired voltage difference between thegate 120 and the nanowire 100. Appropriate choice of materials enablesadvantageous use of the device 90 for transistors and variableresistors.

In another preferred embodiment shown in FIGS. 7A and 7B, a liquiddielectric or combination of solid and liquid dielectrics 110 and 110′,respectively, can be placed between the active segment of the metalnanowire 100 and the gate(s) 120. This would allow for optimal fillingof the dielectric sheath 110 and 110′, while still permitting freemotion of the nanowire surface. Liquid dielectrics have been used inconjunction with some of the previous techniques, in the context ofsingle molecule measurements, as well as for STM measurements of metalcontact transport. In the latter context, they have been shown to havelittle influence on the stability and transport properties of thenanocontact, Liquid dielectrics can have large dielectric constants and,being liquids, would easily adapt to the shape of the nanowire 100,without preventing its deformation. They are thus ideal candidates forthe proposed device 90. For example, the dielectric constant of water atroom temperature is close to 80. While the finite conductivity of watermight be problematic, deionized, water still has a dielectric constantof 15. As another example, glycerol has a dielectric constant above 40.Various oil-based dielectrics [see e.g., U.S. Pat. No. 413,189 which isincorporated by reference herein] have been developed and could besuitable for the device 90. In another preferred embodiment, adielectric gel or sol-gel or a combination of solid and gel dielectricscan be placed between the active segment of the nanowire and thegate(s).

Examples of specific types of the nanowire device 90 are provided below.It is important to note that the device architectures described in theexamples are generic in nature, and do not constitute the exclusiveembodiments of the invention.

Example 1

In one embodiment of the present invention (see FIGS. 6A and 6B), asolid layer of the dielectric sheath 110 is deposited on a substrate 150which has been prepatterned (using standard vapor deposition techniques)with the metallic gate 120 to address the nanowire device 90. The metalnanowire 100 of uniform diameter several tens of nanometers is thendeposited on the surface of the dielectric sheath 110, in alignment withthe submerged electrode forming the gate 120. This fabrication step canbe carried out within standard semiconductor patterning techniques, suchas for example E-beam direct write or alternatively in the long termmasked ion beam lithography. A further layer of solid dielectric 170 isthen deposited on the dielectric sheath 110 fully encasing the nanowire100 (see FIGS. 6A and 6B). A nanoscale pit or cavity 210 is then etchedin the layer of the dielectric 170, exposing the active segment of thenanowire 100 (see FIGS. 6B and 9B). The exposed segment of the nanowire100 is then thinned down to the specified diameter (of order onenanometer) via e.g., focused SEM, chemical etching, or electromigration,or a combination of these techniques.

A hermetic seal can be applied to increase the durability of thenanowire device 90. In one embodiment, a bubble seal (not shown) is usedto enclose an inert atmosphere (e.g., nitrogen or argon) about theexposed segment of the nanowire 100. An epoxy seal for example could beused. Alternatively, in one embodiment, a conventional passivation layer(not shown) over the nanowire device 90 is used to scavenge any smallamounts of oxidant from the sealed environment.

Example 2

In another embodiment (see FIGS. 7A and B), a solid layer of thedielectric sheath 110 is deposited on a substrate 150 prepatterned witha metallic form of the gate 120 to address the nanowire device 90. Ametal nanowire 100 of uniform diameter several tens of nanometers isthen deposited on the surface of the dielectric sheath 110, in alignmentwith the submerged electrode gate 120. This fabrication step can becarried out within standard semiconductor patterning techniques, such asfor example E-beam direct write or alternatively in the long term maskedion beam lithography. A further layer 170 of solid dielectric is thendeposited, as further shown in FIGS. 6A, 6B, 7A, 7B and 9A, fullyencasing the nanowire 100. A nanoscale pit or cavity is then etched inthe dielectric layer 110, exposing the active segment of the nanowire100. The exposed segment of the nanowire 100 is then thinned down to thespecified diameter (of order one nanometer) via e.g., focused SEM,chemical etching, or electromigration, or a combination of thesetechniques.

The nanoscale pit is then filled with liquid dielectric 110′, and asealing cap 160 is applied to the device 90, sealing the liquiddielectric in the pit with the nanowire 100. In this embodiment, severalsuch devices on one chip 200 of the device 90 could be simultaneouslysealed with a single sealing cap 160.

Example 3

In one embodiment of the device 90, a layer of the solid dielectricsheath 110 is deposited on a substrate 150 prepatterned with a metallicform of the gate 120 to address the nanowire device 90. A metal nanowire100 several tens of nanometers in diameter with a “notch” orconstriction at the desired location is then deposited on the surface ofthe dielectric sheath 110, in alignment with the submerged electrodegate 120. This example is similar to that illustrated in FIGS. 6A and6B, but without the additional dielectric layer 170. The nanowire 100 atthe notch can then be thinned down to the specified operating diameterby electromigration. TEM, or chemical etching. The nanowire device 90can then be sealed for durability as described above in Example 1.

Example 4

In another embodiment of the present invention, a solid layer form ofthe dielectric sheath 110 is deposited on the substrate 150 prepatternedwith a metallic form of the gate 120 to address the nanowire device 90.The metal nanowire 100 several tens of nanometers in diameter with a“notch” or constriction at the desired location is then deposited on thesurface of the dielectric sheath 110, in alignment with the submergedelectrode gate 120. The nanowire 100 at the notch can then be thinneddown to the specified operating diameter by electromigration, TEM, orchemical etching. (Various ones of the figures (FIGS. 6A-9B) show thefinished device 90, where the notched nanowire 100 has been thinneddown.) A nanodroplet 230 in liquid form for the dielectric sheath 110 isthen deposited on the surface of the wafer substrate 150, immersing thenanowire device 90 (see FIGS. 5A and 8B). The nanowire device 100,together with the droplet 230, is then hermetically sealed, e.g., withan epoxy seal 160.

Example 5

In one embodiment of the present invention (see FIGS. 9A and 9B) both atop gate 120′ and a bottom gate 120 are included, above and below thenanowire device 90, respectively. The fabrication proceeds as describedin the examples above, but an additional dielectric sheath layer 240 isdeposited above the nanowire device 90, and the top gate 120′ alignedwith the device 90 is patterned by e.g., vapor deposition. Multiplegates may be desirable e.g. to address individual devices in a largearray. For example, if the gate voltage is chosen appropriately, thedevice 90 will switch conducting states rapidly only if the voltage isapplied to both gates.

Because the three terminals of the nanoscale variable resistor arecomprised of metal patterned by standard semiconductor fabricationtechniques, such devices can be readily integrated with conventionalcircuitry on a chip. Because the throughput impedance of such a device90 is on the scale of several hundred to several thousand Ohms,appropriate amplification may be required to interface with standardCMOS circuitry.

In order to individually address distinct devices in a large array on achip, it may be desirable to fabricate a criss-crossing pattern of thetop gate 120 and bottom gate 120 (see FIGS. 10, 11, and 12). With anappropriate choice of operating voltages, only the nanowire device 90located at the intersection of the two active gates 120 and 120′ isaddressed, and caused to switch conducting states.

While preferred embodiments have been illustrated and described, itshould be understood that changes and modifications can be made thereinin accordance with one of ordinary skill in the art without departingfrom the invention in its broader aspects. Various features of theinvention are defined in the following claims.

What is claimed is:
 1. A nanodevice for use in an electrical circuit,comprising: a dielectric having a dielectric constant; a nanowirecoupled the dielectric; and a gate disposed about at least a portion ofthe dielectric and coupled to the nanowire for activating change ofstate for the nanowire, thereby enabling use of the nanowire in anelectronic circuit wherein the nanowire has a length which is changeableto achieve selectable I-V behavior.
 2. The nanodevice as defined inclaim 1 wherein the dielectric constant of the dielectric is greaterthan about
 10. 3. The nanodevice as defined in claim 2 wherein thedielectric is selected from the group consisting of Si, Ge, InSb, InAs,InP, GaSb and GaAs.
 4. The nanodevice as defined in claim 1 furtherincluding a voltage source for applying a potential to the nanowire tochange the length.
 5. The nanodevice as defined in claim 1 furtherincluding a circuit coupled to the nanodevice.
 6. The nanodevice asdefined in claim 5 wherein the circuit comprises an integrated circuit.7. The nanodevice as defined in claim 1 wherein the dielectric comprisesa sheath disposed about the nanowire and a gap positioned between thedielectric sheath and the nanowire.
 8. The nanodevice as defined inclaim 1 wherein the dielectric comprises a sheath disposed about thenanowire and has no gap between the dielectric sheath and the nanowire.9. The nanodevice as defined in claim 7 wherein the dielectric constantis a combination of the dielectric constants of the dielectric sheathand the gap and the dielectric constant is at least about
 10. 10. Thenanodevice as defined in claim 1 wherein the dielectric comprises aliquid.
 11. The nanodevice as defined in claim 10 wherein the liquid isselected from the group consisting of deionized water, glycerol and anoil.
 12. The nanodevice as defined in claim 1 wherein the gate comprisesa metal.
 13. The nanodevice as defined in claim 1 wherein the dielectriccomprises at least one of a gel and a sol-gel.
 14. A method of switchinga nanodevice comprising, providing a nanowire coupled to a dielectric;providing a gate coupled to the nanowire; and applying a voltage throughthe gate to the nanowire to change an electron shell parameter of thenanowire, thereby causing switching of the nanodevice.
 15. The method asdefined in claim 13 wherein the applied voltage comprises an operatinggate voltage V_(g) of about$\left. \frac{e\; V_{g}}{E_{F}} \right.\sim\frac{\alpha\; r_{s}k_{F}R}{6 \in}$to achieve rapid switching.
 16. The method as defined in claim 15wherein the electron shell parameter is changed selectively, therebyenabling switching between different radii for the nanowire whichchanges electrical operating state for the nanowire.
 17. The method asdefined in claim 15 wherein the gate voltage is selected from a group ofa positive voltage to enhance density of carriers in the nanowire andnegative voltage to deplete the density of carriers in the nanowire. 18.The method as defined in claim 14 wherein the nanowire has a lengthwhich is changed by applying a selected voltage, thereby converting thenanowire I-V characteristics to nonlinear behavior.
 19. The method asdefined in claim 14 further including the step of providing thedielectric as a combination of a liquid and solid dielectric, therebyenabling free motion of a surface of the nanowire with respect to thedielectric.
 20. The method as defined in claim 14 wherein the couplingbetween the nanowire and the dielectric comprises a direct contact. 21.A nanodevice for use in an electrical circuit, comprising: a dielectrichaving a dielectric constant; a nanowire coupled to the dielectric; anda gate disposed about at least a portion of the dielectric and coupledto the nanowire for activating change of state for the nanowire; therebyenabling use of the nanowire in an electric circuit; wherein thenanowire has an electron shell system parameter that is changeable uponapplication of a voltage through the gate to control switching of thenanodevice.
 22. The nanodevice as defined in claim 21 wherein thedielectric constant of the dielectric is greater than about
 10. 23. Thenanodevice as defined in claim 21 wherein the dielectric comprises asheath disposed about the nanowire and a gap positioned between thedielectric sheath and the nanowire.
 24. The nanodevice as defined inclaim 21 wherein the dielectric comprises a sheath disposed about thenanowire and has no gap between the dielectric sheath and the nanowire.25. The nanodevice as defined in claim 23 wherein the dielectricconstant is a combination of the dielectric constants of the dielectricsheath and the gap and the dielectric constant is at least about
 10. 26.The nanodevice as defined in claim 21, wherein the nanowire is anelemental metal.
 27. The nanodevice as defined in claim 26, wherein theelemental metal comprises a noble metal.
 28. The nanodevice as definedin claim 26, wherein the nanowire is convertible between linear I-Vbehavior and non-linear I-V behavior.
 29. The nanodevice as defined inclaim 27, wherein the nanowire is convertible between linear I-Vbehavior and non-linear I-V behavior.